Lira Miranda, Bernardita Francisca

Abstract [en]

Asphalt mixture microstructure is formed by aggregates, bitumen binder and air voids. Aggregates make for up to 90% of the mixtures volume and the structure formed by them will depend mostly on their size distribution and shape. The study presented in this thesis has as main objective to develop a framework that allows the characterization of asphalt mixtures based on the aggregates gradation and its impact on pavement performance. Moreover, the study aims to identify the range of aggregate sizes which form the load carrying structure, called Primary Structure, and determine its quality.

The method has been developed as a numerical procedure based on packing theory of spheres. Parameters like porosity, coordination number and disruption factor of the Primary Structure; and a binder distribution parameter for the different sub-structures have been used to evaluate the quality of the load carrying structure and predict the impact on several failure modes. The distribution of bitumen binder has been derived from a geometrical model which relates porosity of the mixture with film thickness of particles considering the overlapping reduction as the film grows. The model obtained is a closer approximation to a physical characteristic of the compacted mixture separated according to different elements of the structure.

The framework has been evaluated on several field and laboratory mixtures and predictions have been made about their rutting performance and moisture resistance. The calculated parameters have compared favourably with the performances reported from the field and laboratory testing. The developed gradation analysis framework has proven to be a tool to identify those mixtures with a poor rutting performance based on the gradation of the aggregates.

The Gradation - Based Framework has satisfactory distinguished between good and bad performance of asphalt mixtures when related to permanent deformation and moisture damage. The calculated parameters have allowed identifying and understanding the main mechanisms and variables involved in permanent deformation and moisture damage of asphalt mixtures. The developed model can be used as a tool to determine the optimal gradation to assure good performance for hot mix asphalt pavements.

Abstract [en]

Aggregates are the major component of asphalt mixtures, greatly influencing the mixtures resistance to failure. The structure that is formed by the aggregates will depend mostly on the size distribution, shape and mineral composition. Coarse aggregate have a strong influence on the resistance to rutting, while fines provide stability to the mixture. In the present study a generalized framework is developed to identify the range of aggregate sizes which form the load carrying structure in hot mix asphalt and determine its quality. The method has been developed as a numerical procedure based on packing theory. Parameters like porosity and coordination number have been used to evaluate the quality of the load carrying structure and relate it to resistance to rutting. The framework has been evaluated on several field and laboratory mixtures and related to their rutting performance. The gradation analysis of the mixtures has compared favorably with the performances reported from the field and laboratory testing. The developed gradation analysis framework has proven to be a tool to identify those mixtures with a poor rutting performance based on the gradation of the aggregates.

Abstract [en]

Film thickness describes the coating around aggregate particles on asphalt mixtures. The standard method of calculating film thickness has proven to present several limitations, such as assuming an average thickness independent of particle size, being completely independent to the porosity of the mixture and considering only one mineral type. In this paper, a binder distribution model is developed for aggregates according to size and role in the structure. The aggregates are separated into two different structures: primary structure, the load bearing one, and secondary structure, smaller material that provides stability to the skeleton. A coating thickness for these two structures is calculated from a geometrical consideration that includes the packing arrangement of particles and the effect of overlapping as the film grows. The results were compared with known rutting performance of field mixtures and moisture conditioned laboratory mixtures, showing a good correlation between film thickness and resistance to failure.